Clarification on Power screw’s specifications please

Hello, I have a power screw. According to the specifications, it is M8x1.25. Does that mean the effective diameter of the thread is 8 mm while the pitch is 1.25 mm? Is the screw radius just 4mm?

From the internet, it looks like the lead angle is atan(Lead/(pi*effective diameter of the thread)) or atan(number of threads*Pitch)/(pi*effective diameter of the thread).

Could you please let me know how to find the number of threads and the lead (m/rev)? What is the lead angle in this case? Thanks in advance.

thnx!

I didn’t find the right solution from the Internet.
References: http://www.engineersedge.com/engineering-forum/showthread.php/4855-Clarification-on-Power-screw-s-specifications-please?s=faa01278f2f992dee52194536fa5ccf3

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